Failure to file excise return

Return filing is mandatory as far as your registration is active.

Though there is no relief in act/rules, you could seek the concenred officer to drop the proceedings as there was no duty liability at all. 

As per geneal principle of any tax law, the penalty can not exceed the tax/duty liability

There are some case laws in your favour too.

Penalty can not be imposed if duty payable is NIL.

So please conveince your excise officers and file return now.